Fish rest but don’t sleep. We sleep, and we have to. There are, however, misconceptions about this vital activity. Some people worry too much about not getting enough sleep. Others try to get along with as little as possible, perhaps spurred on by media reports of successful people who work “18-hour days.”

Example: you hear about somebody who gets by on 4 hours sleep a night, so you decide to train yourself to do that too. After a while, you’re so fatigued all the time you think you must be sick, so you go to the doctor who figures it out right away.

We all hear stories about people who thrive on only a few hours sleep—Edison is said to have slept 4 hours a night, while Einstein needed 12—but even if true, it doesn’t apply to most of us. In general people need 3-5 hours of sleep a night just to sustain life (you are safe, though, if you go even extended periods of little sleep). Most of us want more than that, so we need 5-10 hours for alertness. The average is 7 to 8 hours. Teenagers need to sleep 9 to 9-1/2 hours, but for most adults, less than about 7 or more than about 9 over time is unhealthy. Seniors need the same amount of sleep as other adults, but may have a harder time getting it.

So if you go to bed at 11 and get up at 7, waking up for 5 minutes to go to the bathroom during the night, that’s normal. If you get 7 hours sleep and wake up 2 or 3 times during the night, going back to sleep after 5 minutes, that’s normal too.

You can lose sleep sometimes without dire consequences, but you need a full day’s normal sleep to catch up with each hour lost. Sleep loss is cumulative. Still, you can’t just force yourself to catch up all at once.

Example: you don’t get enough sleep one night and feel tired the next day, so you go to bed at 9 o’clock. You wake up at 4 a.m. and toss and turn until the alarm goes off. Then you complain about waking up at 4 and not being able to get back to sleep. What is wrong? Hint—you already had 7 hours sleep. (These examples are real people, quite intelligent in most matters.)

There’s no need to worry about sleep if you generally get a normal amount and feel refreshed in the morning. Other articles in this series will deal with sleep disorders, ways to get better sleep, and the consequences of sleep deprivation. Good sleep is essential to good health.